CODEWITHSUNDEEP
javafunctional-interface
0seNse0
0seNse0

Reputation: 43

How to replace my old Java code with Optionals (Functional programming)?

How to replace the below code using Java 8 Optionals (Functional programming)?

ClassA classA = dbService.findByA(a);

if (classA == null) {
    classA = dbService.findByB(b);
}

if (classA == null) {
    throw new Exception();
}

return classA;

edit: Maybe if I will make findByA and findByB returning Optional will make my code cleaner using Functional programming?

Upvotes: 3

Views: 138

Answers (3)

Smutje
Smutje

Reputation: 18163

return Optional.ofNullable(Optional.ofNullable(dbService.findByA(a))
    .orElseGet(() -> dbService.findByB(b)))
    .orElseThrow(() -> new Exception());

Or, Java 9, a bit nicer:

Optional.ofNullable(dbService.findByA(a))
    .or(() -> Optional.ofNullable(dbService.findByB(b)))
    .orElseThrow(() -> new Exception());

Upvotes: 3

Olivier Grégoire
Olivier Grégoire

Reputation: 35467

First, make your methods dbService.findByA and dbService.findByB return Optional. That's the basis. If you don't do that, you don't do "functional" programming.

Second, use Java 9+ (or better, the latest version).

Then simply use the following:

ClassA instance = dbService.findByA(a)
    .or(() -> dbService.findByB(b))
    .orElseThrow(Exception::new);

If you're stuck with Java 8, do the following:

ClassA instance = Optional.of(() -> dbService.findByA(a)) // Optional<Optional<ClassA>>
    .orElseGet(() -> dbService.findByB(b)) // Optional<ClassA>
    .orElseThrow(Exception::new);

Upvotes: 1

daniu
daniu

Reputation: 15008

This would work

Optional.ofNullable(
    Optional.ofNullable(dbService.findByA(a))
            .orElseGet(() -> dbService.findByB(b))
).orElseThrow(Exception::new);

I don't think this is much nicer.

Upvotes: 2

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